Bacteria cells, I believe so.
They are buried in the core of the structure.
Hydroponics way of growing, is way of farming, in which plants are grown in nutrient rich water. So, in Hydroponic growing of sprouts, sprouts get their nutrients from the nutrients supply like liquid fertilizers which are mixed with the water. It is one of the advantage of hydroponic means of growing because, unlike in soil system, the plants root does not have to work hard to get nutrient from underground. The easy availability of nutrients and other condition like water, pH level etc makes plants grow faster are fuller.
Also, advancement of technology have made it possible to prepare built-in hybrid hydroponic system which have multiple ways of delivering nutrient to specific plants.
